Sounds like it may have an injector issue. You may want to find a shop capable of testing the injectors and fuel pressure to see if they are all good. Those engines dont like to be run lean or rich, it can damage them internally

Getting white smoke now no more black or blue with it just white when i start the car after about 2 mins it goes very lumpy with lots of white smoke then it will stall.
restart the car still very lumpy with lots of white smoke but no stall second time round car runs fine when warmed up...

Tapping sound at back of rocker cover was located still do not know what it is. if the air pipe is taken the back of the rocker cover the tapping sound is very loud.poss values?

This is the same engine in the picture as mine, this is not my engine in my car.mine is cleaner lol.

Also found a other new problem engine managment light will not come on when turn of key before i turn the engine over, bulb checked and fuse all ok take the fuse out car stops running.is it possible my laguna is in get home mode which will exsplain not reving over 4500 revs hot or cold? (just a tought.)

rocker cover gasket changed, manafold gasket changed, injectors checked did have oil on two of them now clear, fuel air leak fixed glow plugs new, new engine oil , new fuel filter, new oil filter plus all air pipe taken off cleaned and repaired if needed air filter changed.

Have it scanned to see if the computer will communicate first. White smoke isnt a good sign it can be a mixture issue or coolant burning. Does it use any coolant? Especially with it runnning rough, have it chemical tested for a blown head gasket

White smoke is a sign of a bad turbo (a common fault on this vehicle) the not revving over 4000 is also a sign of this ... even though the turbo is not kicking in on tick over it will still cause smoke issue's and the ECU will pick up on the fault, plus you are giving it extra gas/petrol (accelerator pedal) to keep/get it going ... Has the turbo ever been replaced ?? It is very unusual on this model for the turbo to last this long ?? you need to have the turbo checked out ... also the check engine light should be ON all the time ... as jack has suggested, have the vehicle plugged into a diagnostic computer to see if it link's and give's any fault codes .. it could be a bad ECU not controlling some of the system's correctly or a bad sensor not giving the correct signal's causing the ECU to supply wrong information ? .. I do suspect the vehicle is in LIMP mode and will need to be plugged into a computer to verify this ? the tapping sound is probably a sticking valve there are hydraulic lifters on this vehicle !! also as jack suggested this could be a headgasket related issue ... have the cylinders compression tested and a chemical test carried out .. if you have bad compression on any cylinders then this could be a sticking valve on that cylinder or a leaking headgasket !!

If you are not getting any white smoke when the vehicle is at normal operating temperature then I do not believe the turbo is the fault ... you would get more smoke after warm up especially when pressing the throttle ?... but this is also true of a bad headgasket ? have the vehicle plugged into a diagnostic computer to retrieve any fault codes ! and to check the vehicle is in limp mode ... check cylinder compression also ..